Isolating circuit



ISOLATING CIRCUIT Filed Jan. 15, 1964 Francis A.Wi|he|m Richard DMllTOFh INVENTORS.

FIG. 2

United States Patent 3,257,582 ISOLATING CIRCUIT Francis A. Wilhelm andRichard D. Milton, Huntsville,

Ala., assignors to the United States of America as represented by theSecretary of the Army Filed Jan. 13, 1964, Ser. No. 337,509 Claims. (Cl.315171) The invention described herein may be manufactured and used byor for the Government for governmental purposes without the payment ofany royalty thereon.

This invention relates generally to a circuit for isolating a voltagesource from a short circuit path. More particularly, the inventionrelates to a means for isolating and independently controlling the inputand output loops of a high-voltage, high-energy circuit with a sparkgap.

Three electrode gaps have been used to discharge a previously-chargedstorage condenser into a fixed load such as an exploding bridgewire byapplying a very steep high-voltage pulse to a trigger electrode. In thisconventional application of a three-electrode gap the trigger pulsevoltage is chosen so that the sum of it and the condenser voltageexceeds the main gap holdotf voltage. The primary objective here ismicrosecond timing accuracy of the condenser discharge. This applicationof the three-electrode differs in that the objective is to prevent theload (in this preferred embodiment of the invention being a flash lamp)from being short-circuited by a coil within the generator. Essentially,the spark gap must have two distinct holdoff potentials, one high enoughto permit a pre-ionization potential of about 5 kv. to be applied to theflash lamp of a laser device and post-ionization breakdown potential ofabout 1.5 kv. to permit the generator to discharge into the ionizedflash lamp.

Accordingly, it is an object of the present invention to provide anisolating circuit suitable for use in flash lamp circuits.

A further object of the invention is to provide a circuit to prevent aload from being short-circuited by a generator.

A still further object is to provide a circuit with a spark gap meanswhereby a generator may be permitted to discharge into an ionized flashlamp.

These and other objects and advantages of the present invention willbecome apparent from the following detailed description and from theaccompanying drawing in which:

FIGURE 1 shows a schematic circuit diagram according to a preferredembodiment of the invention;

FIGURE 2 shows a schematic diagram of a portion of a second embodimentof the invention; and

FIGURE 3 illustrates a portion of an additional embodiment of theinvention.

Reference numeral 1 denominates a load in the form of a flash lamp whichtakes 5 kv. to ionize. The flash lamp is part of a laser device, notshown, and supplies power thereto. Connected across the lamp by way ofresistor 2 is an ionizing power supply 3. The lamp andv the ionizingpower supply are connected to a common ground.

A three electrode spark gap device 5 is shown as having main electrodesA and B and a control electrode C. Sparking devices of this kind arecommercially available. Electrode B is connected to load 1 by a lead 6.Electrode A is connected to one side of a generator circuit 17 by a lead8. Electrode C of three electrode spark gap 5 is connected to a switch 9by way of a resistor 10.

Three electrode spark gap device 5 is of the type which has two distinctholdoff potentials, one between the main ice electrodes A and B with nopotential supplied to electrode C, and a lower one when there is apotential supplied to electrode C.

Generator 17 consists of a coil 7 having a voltage supply and switchingcircuit 12 connected in parallel to it. The generator of FIGURE '1constitutes an induction power supply and has a low internal impedance.

A condenser 18 (FIGURE 2) having voltage charging circuit 19 connectedin parallel to it may be substituted for the generator 17 of FIGURE 1.Further, a steady state voltage supply 20 (FIGURE 3) may also besubstituted for generator 17 of FIGURE 1.

A potentiometer 13 having slider arm 14 is connected across bias voltagesupply 15 by way of the common ground connections. Slider arm 14 of thepotentiometer is connected to switch 9.

The sequence of operation is as follows:

(a) Initially the generator is at zero potential and thethreshold-control switch 9 is open.

' (b) The flash lamp is now ionized by applying a po tential of about 5kv. and, if necessary, a trigger pulse. At this stage the holdoifpotential across main electrodes A and Bof the spark gap must be above 5kv. to prevent the generator from shorting the flash lamp through itslow impedance to ground.

(c) After the flash lamp ionizes, the potential across the lamp drops toabout 1,000 volts. This is due to the voltage drop across resistor 2when current is being supplied to the ionized flash lamp.

(d) The circuit is now armed by closing switch 9. The breakdown voltagefor the control gap (electrodes A and B) is set, either by mechanicalchoice of the interval or by means of adjusting the bias voltage onelectrode C by potentiometer 13. This breakdown voltage is set to avalue close to, but greater than, the lamp drop (about 1,000 volts). Thelamp is now ready to fire when the generator voltage breaks down themain gap (electrodes A and B).

(e) When the rising generator voltage exceeds the holdoif voltage of thecontrol gap (electrodes A and C), that gap breaks down. The resultantionization sharply drops the holdoff voltage of the main gap and thegenerator discharges through the flash lamp. The value of resistor 10 ischosen to insure ionization without significant load-shunting effect.

The above details the sequence when the generator voltages starts fromzero, as will happen in the circuit of FIG- URE l. The same circuit canbe used to control a voltage source which is a precharged condenser(FIG- URE 2) or steady state generator (FIGURE 3) by opening switch 9 topermit ionizing the lamp or lamps, and discharging the voltage source:by closing said switch 9.

While the invention has been described with reference to a preferredembodiment thereof, it will be apparent that various modifications andother embodiments thereof will occur to those skilled in the art withinthe scope of the invention. Accordingly, we desire the scope of ourinvention to be limited only by the appended claims.

We claim: 7

1. An isolating system comprising a first source of voltage having firstand second terminals, a lamp having third and fourth terminals, aninduct-ion voltage source having fifth and sixth terminals, a threeelectrode gap means having seventh, eighth, and ninth terminals, meansconnecting said first, third, and seventh terminals to each other, meansconnecting the eighth and fifth terminals to one another, further meansconnecting said second, fourth, and sixth terminals to each other, and afurther source of voltage connected between said ninth terminal and saidsixth terminal.

2. An isolating system comprising a first source of voltage having firstand second terminals, a lamp having third and fourth terminals, aprecharged condenser voltage source having fifth and sixth terminals, athree electrode gap means having seventh, eighth, and ninth terminals,means connecting said first, third, and seventh terminals to each other,means connecting the eighth and fifth terminals to one another, furthermeans connecting said second, fourth, and sixth terminals to each other,and a further source of voltage connected between said ninth terminaland said sixth terminal.

3. An isolating system comprising a common lead,'a first source ofvoltage having one side connected to said common lead, and having firstconnecting means connecting its other side to an output terminal, lampmeans connected between said output terminal and the common lead, aninduction voltage source, a three-electrode spark gap means having amain gap and a control gap, second connecting means connecting theinduction voltage source, the lamp means, and the main gap in a firstseries circuit,

a source of bias voltage, a switch means, and third connecting meansconnecting said source of bias voltage, said switch means, said controlgap, and said induction voltage source in a second series circuit.

4. A system as set forth in claim 3, wherein said lamp means is a flashlamp of a laser device.

5. A system as set forth in claim 3, wherein said first connecting meansis a resistor.

References Cited by the Examiner UNITED STATES PATENTS 2,596,142 5/1952Gerwin 315230 X 2,829,315 4/1958- Hoekstra 315208 2,870,379 1/1959 Bird315-'-176 X JOHN W. HUCKERT, Primary Examiner. D. O. KRAFT, AssistantExaminer.

1. AN ISOLATING SYSTEM COMPRISING A FIRST SOURCE OF VOLTAGE HAVING FIRSTAND SECOND TERMINALS, A LAMP HAVING THIRD AND FOURTH TERMINALS, ANINDUCTION VOLTAGE SOURCE HAVING FIFTH AD SIXTH TERMINALS, A THREEELECTRODE GAP MEANS HAVING SEVENTH, EIGHTH, AND NINTH TERMIALS, MEANSCONNECTING SAID FIRST, THIRD, AND SEVENTH TERMINALS TO EACH OTHER, MEANSCONNECTING THE EIGHTH AND FIFTH TERMINALS TO ONE ANOTHER, FURTHER MEANSCONNECTING SAID SECOND, FOURTH, AND SIXTH TERMINALS TO EACH OTHER, AND AFURTHER SOURCE OF VOLTAGE CONNECTED BETWEEN SAID NINTH TERMINAL AND SAIDSIXTH TERMINAL.